1. Field of the Invention
This invention relates to a process for the preparation of 7-amino-cephem compounds. More particularly, this invention is concerned with a process for the preparation of 7-amino-cephem compounds of the general formula I ##STR4## wherein X stands for a hydroxyl group, an acetoxy group or a thiosulfuric acid residue, which process is characterized by subjecting a homologue of cephalosporin C of the general formula II: ##STR5## wherein R.sub.1 stands for hydrogen, a lower alkanoyl group, an arylalkanoyl group, an alkoxycarbonyl group, a lower haloalkoxycarbonyl group a substituted or unsubstituted aroyl group, a N-arylcarbamoyl group or a substituted or unsubstituted aryl group, R.sub.2 either means hydrogen or forms, together with the ##STR6## group, a phthalimido group, and X stands for a hydroxyl group, an acetoxy group or a thiosulfuric acid residue, to an enzymatic action of the cultured mycelia of mold fungi or the secondary preparation therefrom.
For simplicity, the 7-amino-cephem compounds of the general formula I are hereinafter often referred to as "7-amino-cephem compounds I", and the homologues of cephalosporin C of the general formula II as compounds II".
2. Prior Art
Useful antibiotics of the cephalosporin series, such as, for example, Cephalothin, Cephaloridine or Cephaloglycine, are prepared in general by converting cephalosporin C which is obtained by the fermentation process, into 7-amino-cepharosporanic acid (hereinafter often referred to as "7-ACA") and chemically modifying the latter in an appropriate manner. Therefore, the 7-ACA compound is the most important starting material for the preparation of these cephalosporin antibiotics. Further, both Cefoxitin which is now under development as a new synthetic cephalosporin antibiotic and which is attracting public attention due to excellent effects exhibited in its evaluation testing (see Antimicrobial Agents and Chemotherapy, Vol. 5, page 25, 1974) and Cefuroxime which also is now under development and whose effects are recognized as excellent (see The Journal of Antibiotics, Vol. 29, page 29, 1976), have commonly carbamoyloxymethyl groups in the 3-positions. For the synthesis of such compounds, 3-deacetyl-7-amino-cephalosporanic acid (hereinafter often referred to as "D-7-ACA") serves as a better starting material. The D-7-ACA is also suitable as the starting material for the synthesis of 3-substituted-vinyl-cephalosporine which is attracting public attention due to their potent antibacterial effect on Gram negative bacteria (see Journal of Medical Chemistry, Vol. 18, page 986, 1975).
A number of methods for effecting in chemical manner the deacylation of cephalosporin C at the 7-position (hereinafter often referred to, for simplicity, as "deacylation") have been hitherto proposed, and in fact the deacylation is at present carried out by chemical processes on an industrial scale. As a method for chemical deacylation of cephalosporin C is known, for example, the iminohalide process (see Japanese Patent Publication No. Sho-41-13862). This deacylation process comprises the steps of; protection of the amino group of cephalosporin C; protection of the carboxyl group; conversion to the iminochloride; conversion to the imino ether; deacylation; and elimination of the protective group for the carboxyl group. Since this process involves a number of reaction steps, sequential operation of the steps is very cumbersome, taking a long period of time. Further, in an attempt to improve the iminohalide process was proposed the so-called silyl chloride process (see Japanese patent Publication No. Sho-45-40899). This process is advantageous over the iminohalide process in that the process steps are fewer in number, but is accompanied by problems such as a requirement of cooling to temperatures below -60.degree. C. and high cost of the reaction apparatus and so on. In addition to these problems, the chemical deacylation processes suffer from another disadvantage that it is necessary in order to attain high yields to use high purity starting material cephalosporin C.
The theoretical possibility of the direct deacylation of cephalosporin C by the use of microorganisms or enzymes seems to be suggested from experience in the preparation of 6-amino-penicillanic acid (6-APA) from penicillin. However, no reports on the production of 7-ACA or D-7-ACA from cephalosporin C on an industrial scale have been hitherto made. It is theorized that this is due to the fact that the specific group (i.e. D-5-amino-5-carboxy-pentanoyl group) is present in the side chain in the 7-position of cephalosporin C, and thus it would be expected that it would be difficult or impracticable to carry out the direct deacylation enzymatically.
In U.S. Pat. No. 3,239,394 a process is proposed for the preparation of 7-ACA from cephalosporin C by the use of microbial cells. This process involves treating cephalosporin C with the cultivated cells of a certain strain of bacterium selected from the group belonging to the genera Brevibacterium, Achromobacterium, and Flavobacterium to form 7-ACA and D-7-ACA in the reaction mixture. With such a process, however, it would be difficult to expect an improvement in reaction yield due to the fact that the strains of the microorganisms used are of extremely weak deacylation activity and also the fact that the enzyme with the deacylation activity has .beta.-lactamase activity as well, thus causing the cleavage of the .beta.-lactam rings of both cephalosporin C and the product 7-ACA thereof.